Crop reads an
image(7)
file (default standard input), crops it, and writes it as a compressed
image(7)
file to standard output.
There are two ways to specify a crop, by color value or by geometry.
They may be combined in a single run of
crop, in which case the color value crop will be done first.

The
-c option takes a red-green-blue triplet as described in
color(3).
(For example, white
is
255255255.) The corresponding color is used as a value to be cut from the outer
edge of the picture; that is, the image is cropped to remove the maximal
outside rectangular strip in which every pixel has the specified color.

The
-i option insets the image rectangle by a constant amount,
n, which may be negative to generate extra space around the image.
The
-x and
-y options are similar, but apply only to the
x or
y coordinates of the image.

The
-r option specifies an exact rectangle.

The
-t option specifies that the images coordinate system should
be translated by
tx,
ty as the last step of processing.

The
-b option specifies a background color to be used to fill around the image
if the cropped image is larger than the original, such as if the
-i option is given a negative argument.
This can be used to draw a monochrome frame around the image.
The default color is black.

Iconv changes the format of pixels in the image
file (default standard input) and writes the resulting image to standard output.
Pixels in the image are converted according to the channel descriptor
chandesc, (see
image(7)).
For example, to convert a 4-bit-per-pixel grey-scale image to an 8-bit-per-pixel
color-mapped image,
chandesc should be
m8. If
chandesc is not given, the format is unchanged.
The output image is by default compressed; the
-u option turns off the compression.